Asynchronous DNS Resolution

amphp/dns provides asynchronous DNS name resolution for Amp.

Installation

composer require amphp/dns

Usage

Configuration

amphp/dns automatically detects the system configuration and uses it. On Unix-like systems it reads /etc/resolv.conf and respects settings for nameservers, timeouts, and attempts. On Windows it looks up the correct entries in the Windows Registry and takes the listed nameservers. You can pass a custom ConfigLoader instance to BasicResolver to load another configuration, such as a static config.

It respects the system’s hosts file on Unix and Windows based systems, so it works just fine in environments like Docker with named containers.

The package uses a global default resolver with can be accessed and changed via Amp\Dns\resolver(). If an argument other than null is given, the given resolver is used as global instance. The instance is automatically bound to the current event loop. If you replace the event loop via Amp\Loop::set(), then you have to set a new global resolver.

Usually you don’t have to change the resolver. If you want to use a custom configuration for a certain request, you just create a new resolver instance and use that instead of changing the global one.

Address Resolution

Amp\Dns\resolve provides hostname to IP address resolution. It returns an array of IPv4 and IPv6 addresses by default. The type of IP addresses returned can be restricted by passing a second argument with the respective type.

// Example without type restriction. Will return IPv4 and / or IPv6 addresses.
// What's returned depends on what's available for the given hostname.

/** @var Amp\Dns\Record[] $records */
$records = yield Amp\Dns\resolve("github.com");
// Example with type restriction. Will throw an exception if there are no A records.

/** @var Amp\Dns\Record[] $records */
$records = yield Amp\Dns\resolve("github.com", Amp\Dns\Record::A);

Custom Queries

Amp\Dns\query supports the various other DNS record types such as MX, PTR, or TXT. It automatically rewrites passed IP addresses for PTR lookups.

/** @var Amp\Dns\Record[] $records */
$records = Amp\Dns\query("google.com", Amp\Dns\Record::MX);
/** @var Amp\Dns\Record[] $records */
$records = Amp\Dns\query("8.8.8.8", Amp\Dns\Record::PTR);

Caching

The BasicResolver caches responses by default in an Amp\Cache\ArrayCache. You can set any other Amp\Cache\Cache implementation by creating a custom instance of BasicResolver and setting that via Amp\Dns\resolver(), but it’s usually unnecessary. If you have a lot of very short running scripts, you might want to consider using a local DNS resolver with a cache instead of setting a custom cache implementation, such as dnsmasq.

Reloading Configuration

The BasicResolver (which is the default resolver shipping with that package) will cache the configuration of /etc/resolv.conf / the Windows Registry and the read host files by default. If you wish to reload them, you can set a periodic timer that requests a background reload of the configuration.

Loop::repeat(60000, function () use ($resolver) {
    yield Amp\Dns\resolver()->reloadConfig();
});

The above code relies on the resolver not being changed. reloadConfig is specific to BasicResolver and is not part of the Resolver interface. You might want to guard the reloading with an instanceof check or manually set a BasicResolver instance on startup to be sure it’s an instance of BasicResolver.